Hi guys,
How can I help with this, I still teach electrical engineering at the University of Nebraska, and before that I have about 25 years in the field. Mostly embedded microcontrollers and stuff. I do have several XOs to work with. I would have jumped in earlier but the end of the semester is a bit hectic. Mark On May 10, 2009 Sunday, at 4:13:47:0, C. Scott Ananian wrote: > On Sun, May 10, 2009 at 5:01 PM, Reinder de Haan <r...@mveas.com> wrote: >> C. Scott Ananian wrote: >>> On Wed, May 6, 2009 at 6:14 PM, Reinder de Haan <r...@mveas.com> >>> wrote: >>>>> Absolutely not. The A/D is eight bits, with an input range >>>>> spanning >>>>> 0 - 3.3V, so the best you >>>>> can hope for is about 13 mV per LSB. I would guess actual >>>>> accuracy >>>>> to be closer to 26 mV. >>> >>> I think the actual A/D reference voltage is probably *maximum* 3.3V. >>> What's the *minimum* A/D reference voltage? And can the A/D measure >>> all the way down to ground? (Sometimes there's a Vmin for the A/D >>> input, often around a diode drop above ground.) >>> >>>> i did some more experiments and at ~20 cm from the halogen lamp i >>>> doest >>>> matter is i turn the backlight full on of off .. i dont have color >>>> anymore.... >>>> at that distance the bare led gave about 250mv (maybe a bit more >>>> into a >>>> very high R fet gate...) >> >> >> that 250mv is without the light guide and lcd cover installed! >> with the light guide in place its more like ~70mv ... >> 0.07/3.3*256= 5.4 LSB and then the Rin of the ADC must be >10Mohm... > > 5 LSB is still okay, and it could be more if the A/D Vref can be > dropped below 3.3V. > --scott > > -- > ( http://cscott.net/ ) > _______________________________________________ > Devel mailing list > Devel@lists.laptop.org > http://lists.laptop.org/listinfo/devel _______________________________________________ Devel mailing list Devel@lists.laptop.org http://lists.laptop.org/listinfo/devel
